The bird, which was missing his left leg and foot, was part of the Aransas-Wood Buffalo population, the only natural wild flock of whooping cranes. The most recent estimation of the flock is 279 birds, according to the news release.

The amputated leg had started to heal over, but biologists worried about the right foot, which had started to show lesions and wear from overcompensation, said Wade Harrell, whooping crane recovery coordinator for the U.S. Fish and Wildlife Service.

How the leg and foot were injured is not evident, but it could have been a predator attempting to grab the bird, Harrell said.

According to the news release, the bird was treated by zoo staff for 30 days. The exact cause of the bird's death is unknown, said Tracy Levine, San Antonio Zoo bird department II supervisor. She said an initial report and appropriate samples have been sent to a pathologist, who will make a determination of the cause of death. The results can take several weeks, she said.

Levine said the amputation of the bird's lower left leg was considered a severe, traumatic injury that potentially could lead to illness or other complications as a result of the stress that was placed on the bird's system.

She said the bird had been showing much improvement with his appetite and became more relaxed around keepers, who entered his enclosure to feed and service the area. The bird maintained the same disposition and activity level during his stay at the zoo, and a decrease in activity was not observed until the morning of his death, she said.

"All the bird keepers and supervisors that spent many hours caring for and observing this bird quickly became attached to this beautiful and amazing bird," Levine said.

She said the crane was nicknamed "Trooper" for all he had endured.

"We were all very saddened by his death but feel confident we provided him with the best possible care while he was housed at our facility," Levine said.